North America Distribution

Facts About

Giant knotweed is an aggressive invader, similar to Japanese knotweed. It was first introduced as a garden ornamental in 1894, and was later used for erosion control. Giant knotweed has since been declared a noxious weed in some states. It can grow over twelve feet tall and forms dense stands that exclude all other vegetation.

Habitat

Anthropogenic (man-made or disturbed habitats), meadows and fields, shores of rivers or lakes

Characteristics

Habitat

terrestrial

wetlands

New England state

Connecticut

Maine

Massachusetts

Rhode Island

Vermont

Flower petal color

green to brown

white

Leaf type

the leaves are simple (i.e., lobed or unlobed but not separated into leaflets)

Leaf arrangement

alternate: there is one leaf per node along the stem

Leaf blade edges

the edge of the leaf blade is entire (has no teeth or lobes)

Flower symmetry

there are two or more ways to evenly divide the flower (the flower is radially symmetrical)

6×7.
Fallopia japonica
×
Fallopia sachalinensis
→Fallopia×‌bohemica
(Chrtek & Chrtková) J.P. Bailey is an uncommon knotweed hybrid known from
CT, MA, ME,
RI,
VT. It is becoming increasingly more frequent on the landscape. Its leaf morphology is intermediate between
F. japonica and
F. sachalinensis (i.e., they tend to be large and are truncate to cordate at the base). The best discriminating character is the minute, but firm, stoutly conical, 1- or 2-celled hairs found on the abaxial leaf surface (this type of hair not found in the parental taxa; view at 20
× or higher) [Fig. 788, M].